Unfortunately (and at least right now), Tasks only work with Component or of course Component derived types. Everything in Tasks in regards to “Agent” is made with the agent being a Component derived type and thus Component is the lowest hierarchy type a Task agent can be assigned.
This might change in the future, but right now at least is unfortunately not possible to use ScriptableObject for a Task agent.
For your particular case, I would suggest to please create a custom condition task which will have a public fied of your ScriptableObject type, subscribe to your event and use it accordingly. It is very easy to create such a task. Here is an example: